Definition of Test Cross

A test cross is a tool that helps us in exploring the genotype of the organisms. In the beginning, it was used in order to determine the alleles which were present in the genotype. As we know that the organism’s genetic makeup is termed as its genotype and this includes all the alleles that are carried by the organism. In this way, the test cross enables us to determine whether the dominant phenotype is homozygous for a certain allele or heterozygous.

When the test cross is performed, the test individual is allowed to breed with an individual that is homozygous for the recessive trait. The recessive individual can only pass down the recessive alleles, hence the test individual determines the phenotype of the offspring. The test cross leads to two possible results.

One is that if all the offspring produced by the test cross express the dominant trait, then the test individual is homozygous for the dominant allele. On the other hand, if any of the offspring express the dominant trait, then the test individual is heterozygous for the dominant allele.